By Stacy Palen

This week, I draw your attention to this piece of news that neatly encapsulates many of the concepts that you might be teaching at this point in the semester! Betelgeuse’s recent variability may be caused by dust and pulsation—so no nearby supernova in the works for us this year. That’s typical 2020 for you right there. Disappointing, all around.

Below are some questions to ask your students based on this article.

1) Why were astronomers, earlier in the year, talking about Betelgeuse exploding as a supernova sometime soon?

Answer: Because it had abruptly become dimmer, and evolution to supernova was one possible explanation.

2. What key conclusion in this most recent study definitively rules out the supernova-soon scenario?

Answer: Betelgeuse is still fusing helium in its core, which means that it has a significant amount of time left before it makes the full, onion-like set of fusion shells that precede a supernova.

3) Typically, astronomers first determine the distance to a star and then infer its size from knowing something about its evolutionary state and where it sits on the H-R Diagram. What did astronomers do differently in this study?

Answer: In this study, astronomers used stellar seismology to find the size of the star first and then worked backwards to determine the distance. This distance agrees (it is within the error bars) with previously determined distances to Betelgeuse.

4) Will Betelgeuse eventually explode as a supernova (even if we don’t get to see it this year)?

Answer: Yes, because it is a red supergiant.

5) Will that affect life on Earth?

Answer: Probably not. It is too far away to have an impact on life on Earth, although it would become incredibly bright for a short time.

By Stacy Palen

Titan’s orbit is growing, which is unexpected! This article might be appropriate when discussing orbits, outer planet moons, or resonances.

Below are some questions to ask your students based on this article.

1) What did astronomers EXPECT to find out about Titan’s orbit, before undertaking this study?

Answer: They expected to see that Titan’s orbit was unchanging.

2) How much does Titan’s orbit grow each year? Give an example of a common, everyday object that is about that size.

Answer: 11 centimeters (cm). This is a little bit shorter than a pen or pencil, so each year, Titan’s orbit grows by less than a pencil length.

3) Compare this rate to the rate at which the orbit of Earth’s Moon grows. Is Titan moving away from Saturn faster or slower than the Moon moves away from Earth?

Answer: The Moon moves away at 4 cm per year. Titan moves away from Saturn almost three times faster.

4) For how many years did the Cassini spacecraft orbit Saturn?

Answer: Cassini orbited from 2004 to 2017, so approximately 13 years.

5) During that time, how much did Titan’s orbit expand in total?

Answer: 11 cm times 13 years is 143 cm, just shy of 1.5 meters.

6) The semi-major axis of Titan’s orbit is 1,221,870,000 meters. By about what fraction did this value grow during Cassini’s visit to Saturn?

Answer: 1.43 m / 1.22187 X 109 m is about 1 in a billion. Dang.

7) What is “resonance-locking tidal theory?” How does this account for the loss of energy from Titan’s orbit, due to the orbit growing larger?

Answer: This is the idea that if the moon tidally flexes Saturn, in resonance with Saturn’s internal ringing, energy can be transferred from the moon’s orbit to Saturn’s internal motion.

What other questions would you ask your students based on this article? Feel free to leave suggestions in the comments!

ESO/P. Vernazza et al./MISTRAL algorithm (ONERA/CNRS)

By Stacy Palen

According to this article by the ESO, Hygiea has been imaged by ESO’s VLT. It is round, which makes it a dwarf planet rather than an asteroid. Smaller than Ceres, it is now the smallest known dwarf planet in the Solar System.

1) Study the image of Hygiea at the top of the article. The image of this tiny object is a little bit fuzzy, despite the powerful telescope used to obtain it. Nonetheless, some features are visible. Describe the surface of Hygiea.

Hygiea appears to have some craters, with variations in height as well as variations in brightness.

2) Until this image was taken, astronomers were not sure whether to categorize Hygiea as an asteroid or a dwarf planet. Which criterion for dwarf planet status could be determined from this image?

Hygiea has enough gravity to pull itself into a round shape.

3) The article compares Hygiea’s size (430 km) to that of both Pluto (2400 km) and Ceres (950 km). Roughly how many times larger are these other dwarf planets than Hygiea?

Ceres is a bit more than twice as large, and Pluto is about six times larger.

4) Describe the origin of this dwarf planet, in your own words.

A much larger planetesimal collided with a smaller one about 2 billion years ago. The explosion created 7,000 asteroids, at least one of which had enough gravity to form a dwarf planet.

Stocktrek Images, Inc./Alamy Stock Photo

By Stacy Palen

Fast radio bursts have been known since 2007. Recently, China’s FAST telescope has detected a repeat of one first discovered at Areceibo in 2012. This article poses several explanations for fast radio bursts.

Questions:

1) Study the picture of the 500-m telescope at the top of the article. Is this a “steerable telescope?"

Answer: No, this telescope is far too large to be steerable.

2) Describe how a telescope that is not steerable “sees” the sky differently than a steerable telescope.

Answer: A telescope like this can see only the portion of the sky that passes through its zenith. Because it is not steerable, it cannot track an object, so the observing time is set by the amount of time it takes for the object to pass through the field of view.

3) The signal was emitted from a source 3 billion light-years away. How long has the signal been travelling to reach us?

Answer: The signal has been traveling for three billion years.

4) What was happening on Earth when this signal left the source?

Answer: The earliest forms of photosynthesis date from around this time.

5) Why is a repeating FRB so interesting to astronomers?

Answer: If the FRB repeats, that rules out a whole class of causes. The object has clearly not blown up, so this is not connected to supernovae or black hole mergers.

6) Choose one of the proposed explanations for FRBs and explain in more detail how an FRB could be caused in that way.

Answer: Answers will vary.

Image credit: NASA/JPL-Caltech

By Stacy Palen

Sgr A* is flaring to twice peak historical levels, possibly because of gravitational disturbance from S0-2. This particular article from Vice News provides a good opportunity to help students see when they are being “click-baited,” since “Nobody Knows Why” is a bit of a tease. There are actually several explanations for why this might happen, as the article later explains.

1) “Flux” may be a new vocabulary word, particularly in this context. Look it up and summarize the definition that is relevant to this article in your own words.

Flux is the light emitted per second per square meter.

2) The article states that we have been monitoring Sgr-A* for about 20 years. What technological improvements made a monitoring campaign like this one possible?

We needed to be able to observe in the infrared at high enough resolution to avoid confusion of sources in this tightly packed region of the Galaxy.

3) What possible causes for the flare are given in the article?

A close pass of SO-2 may have disturbed the gas near the black hole. We may be seeing a delayed reaction from a dust cloud that passed by and was torn apart.

4) Notice the article’s title: “…and Nobody Knows Why”. Do you think that this is an accurate characterization of what astronomers know about this flare? Why do you think the article’s title was written in this way?

Answers will vary for the first question; the second answer should include something about baiting people to click on the story.

By Stacy Palen

Remnants of the lost city of Cahokia. Credit: Steve Moses/Flickr (CC BY 2.0)

In this article from Scientific American, a climate scientist talks about why she is not reassured by the idea that “the climate has changed before.” This is an opinion piece, but it is worth a read if you have students who raise this argument.

1) The author points out that climate has changed many times in the past. Does that imply that Earth’s climate is sensitive to small changes or insensitive to small changes?

It implies that Earth’s climate is very sensitive to small changes.

2) This scientist is making the case that historical climate change has had dramatic and long-lasting effects on human communities. Do they provide evidence to support this argument?

Yes. The author mentions many examples, from both prehistoric and historic times.

3) The author also makes the case that many factors contributed to these effects. Identify an example of a pre-existing condition that was made worse by natural climate change.

Answers vary, but the overextended Roman empire or inequality in France might be mentioned.

4) Do you see any evidence for a similar pre-existing condition in the country today? Explain.

Answers will obviously vary depending on where you live. This is a small test of how well-informed students are about what’s happening in the larger society.

5) Describe how climate change might impact the condition you noted in (4).

Answers will vary, but should be consistent with their answer to 4. So, for example, if they mention immigration, they might include here a mention of how drought drives migratory patterns.

6) In your own words, explain the argument this scientist proposes that historical climate change should be seen as concerning rather than reassuring.

Answers will vary based on the students’ comprehension of the post.

By Stacy Palen

Summary: Hayabusa2 has been investigating the asteroid Ryugu. This is a sample-return mission, which has implications for Solar System formation and may cast light on the origins of life on Earth.

Article: Japan (Very Carefully) Drops Elastic Explosives Onto an Asteroid

1. Consider what you know about the origin of the Solar System. What are astronomers hoping to learn from Hayabusa2’s mission to Ryugu?

Answer: They are hoping to learn about the composition of matter in the Solar System when it formed. This could confirm or refute our ideas about Solar System formation and the formation of the asteroid belt. The precursor molecules for life are also present on the asteroid, which may give us clues about the origins of life on Earth.

2. The article states that Hayabusa2 “physically touched down” on Ryugu in February 2019, and took a sample of dust kicked up. Go online and read more about it. Describe this event in more detail. Do you consider “physically touched down” to be an accurate characterization of what happened?

Answer: The spacecraft approached the surface and shot a small projectile into the asteroid. A sampler horn collected the kicked up dust and the spacecraft moved on. This is not quite what’s implied by the summary sentence in the news article.

3. Ryugu is less than a mile across, in an orbit between Earth and Mars. Using an average orbital radius between those two planets (1.25 AU), find the orbital period of Ryugu. Convert this orbital period to seconds.

Answer: This is a review of Kepler’s third law. The period is 1.16 years, which equals 3.7 X 10⁷ seconds.

4. The circumference of Ryugu’s orbit is 1.2 X 10¹² Divide this distance traveled by the period to find the speed of the asteroid in its orbit. This is the speed that Hyabusu2 must be traveling in order to rendezvous with the asteroid.

Answer: This is a reminder of the definition of the properties of an orbit (what is the circumference, and what is the period). The speed is 32,000 m/s.

5. When was the spacecraft launched, and when is the sample return mission expected to arrive back here on Earth?

Answer: The spacecraft launched in December 2014, and will return a capsule to Earth in December 2020.

Image Contributor: Mark Garlick/Science Photo Library, 1 March 2013

Credit: Sloan Digital Sky Survey, www.sdss.org

Once in a while something new happens. In the case of an article published in The Atlantic, astronomers observed an object that had properties like those of a supernova explosion, but much too fast. That led to some detective work across the electromagnetic spectrum to try to figure out what was happening!

1. What event triggered astronomers to pay attention to this particular location in space?

Answer: A bright spot appeared where none had been before.

2. How did astronomers communicate with each other that something interesting was happening?

Answer: They used The Astronomer’s Telegram, a global astronomy alert system.

3. Where did the event happen?

Answer: This event occurred in a nearby galaxy. It was detected at a telescope in Hawaii. (Note: I would use answers to this question to find out if students have sorted out what an “event” is, and the difference between an “event” and the detection of it.)

4. What about this event made it clear that this was not a “normal” supernova?

Answer: It was too bright, and also faded away too quickly. This is weird because brighter supernovae should fade away more slowly, not more quickly.

5. What is the current working hypothesis about what happened in the event?

Answer: Astronomers think this may have been the formation of a black hole or a neutron star.

6. How will astronomers test this hypothesis?

Answer: This event is over, so astronomers will have to wait for another one to occur to test their ideas against observations of that future event.

Image Credit: Emmanuel Masongsong/UCLA EPSS/NASA

By Stacy Palen

In January, geologists updated the model of Earth’s magnetic field, a year ahead of schedule.

1. Study the map titled “Magnetic Motion.” How much time separates each pair of red dots between 1900 and 2010?

Answer: The dots indicate 10-year time intervals until 2010. There is an extra dot placed for 2015.

2. In general, how does the movement of the magnetic pole since 1990 compare to the movement of the pole prior to that time?

Answer: Because the red dots are much farther apart after 1990, we can conclude that the pole is moving a lot faster in the last few decades than it did prior to that.

3. Why do we care about what happens to the magnetic pole of Earth?

Answer: The position of the magnetic pole underlies all navigation. If we don’t know where the pole is, we don’t know where we are.

4. Why did geologists decide to update the model a year earlier than expected?

Answer: Because the position of the pole was changing so fast that navigation was becoming inaccurate.

5. What is the working hypothesis for why the position of the magnetic pole is changing so rapidly right now?

Answer: A jet of liquid iron is weakening the magnetic field in Canada. This means that a second patch of magnetic field in Siberia is relatively stronger, so the pole is moving in that direction.

6. How does this news article relate to what you have learned about Earth’s magnetic field?

Answer: We have learned that Earth’s magnetic field changes over time, and that the history of those changes are recorded in rocks. We have also learned that the magnetic field affects the aurorae in Earth’s atmosphere. As the magnetic field changes, this should affect the aurorae as well.